I think your best shot would be to find a pro domina which lists FT session and multi domme session in her practices. Then you could ask her for a pro-domme friend of her who like FT too to join her for the session.

I've found this thread that maybe can help you: http://www.maxfisch.com/thehang/ubbthreads.php/topics/1626834/Best_Domme_for_Full_Toilet_in_
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